Boost rectifiers are well known and widely used for universal ac line (e.g. 85-265 Vac) applications. Unfortunately, when the input voltage of boost rectifier circuit is at its low-line conditions (e.g. 85-135 rms Vac) the power loss of the boost rectifier circuit is significantly higher than when the input voltage is at its high-line conditions (e.g. 170-265 rms Vac). This power loss results because of the high input current to the boost rectifier circuit and high switch duty cycle for the boost switch that result from the low-line input conditions. If MOSFETs are used as the boost switch, its conduction loss can be more than 40 times higher at an input of 85 rms Vac than at an input of 265 rms Vac. Further, the diode loss in the rectifier bridge is also very high at low line.
Voltage doubling circuits have been proposed to increase the efficiency of boost rectifiers by reducing the discharge voltage of the boost inductor at low line. This improved efficiency is accomplished by the use of relays which are switched between low-line and high-line conditions. Because the switch duty cycle is reduced the rms current of the switch in the boost doubler circuit is reduced compared to a conventional boost rectifier. However, losses at low-line inputs, though reduced, are still high compared to losses under high-line input conditions.
A boost rectifier circuit is needed to reduce losses at low-line input conditions and achieve improved efficiency.